Ring-shaped transducer



`luly 21, 1964 w. T. HARRIS 3,142,035

RING-SHAPED TRANSDUCER Filed Feb. 4, 1960 4 She'ets-Sheet 1 imi July 21,1964 w. T. HARRIS 3,142,035

RING-SHAPED TRANSDUCER Filed Feb. 4, 1960 4 sheets-sheet 2 INVENTOR July21, 1964 w. 1'. HARRIS RING-SHAPED TRANSDUCER 4 Sheets-Sheet 3 FiledFeb. 4, 1960 FIG. 5

INVENTOR. Maig/,e z' wwf/S )www July 21, 1964 w. T. HARRIS 3,142,035

RING-SHAPED TRANSDUCER Filed Feb. 4, 1960 4 Sheets-Sheet 4 pas3,142,035' RING-SHAPED TRANSBUCER Wilbur T. Harris, Woodbury, Conn.,assigner to The Harris Transducer Corporation, Woodbury, Conn., acorporation of Connecticut Fiied Feb. 2-, 1969, Ser. No. 6,722 leClaims. (Cl. Seil-l) This invention relates to the construction of atransducer particularly adapted for the reception and transmission ofvibrations in the sonic and ultrasonic ranges.

Transducers capable of operating in these frequency ranges, and capableof handling vibrations at appreciable power levels, are oftencylindrical in configuration, and formed of a plurality of transducingelements, usually in the form of elongated strips, which are assembledt0- gether to produce a substantially ring-shaped structure. Thesedevices have suffered from a number of substantial drawbacks which havebeen made for difiiculties and expense in assembly and operation.

One of these drawbacks resides in the fact that the resonant frequencyof such transducers is ordinarily controlled almost exclusively by theirsize. For a resonant frequency of 5 kc., a typical such transducer isone foot in diameter, while for a resonant frequency of 500 cycles thediameter would have to be increased to something on the order of l0feet. The construction of the instant invention permits attainment, witha given size transducer, of lower resonant frequencies than haveheretofore been possible.

A second drawback of the prior art structures revolves about thedifliculty of assembling the various strips which make up the completetransducing unit and reliably securing them in assembled condition. Evenwith special assembling fixtures, it has proved to be practicallyimpossible on a production basis to form the ring-like structure bysecuring strips to one another in proper positional relationship. In thecourse of assembly the various individual strips must be tightly pressedagainst one another with their films of bonding agent therebetween, thebonding agent being subsequently hardened. The very act of pressing thestrips against one another has with prior art constructions tended tocause one or more of the strips to shift from its proper position. Aring-like structure of uncertain or variable periphery and withdiscontinuities in circumferential connection tends to result. Thestructure of the present invention permits the ready assembly of thestrips into a ring-like structure to accurately predeterminedconfiguration, the various strips being so shaped as to cooperate withone another and hold one another in place when they are pressedtogether.

In prior art constructions, the strips of transducing material are ofappreciable peripheral length. This poses an electrical andelectro-mechanical problem. The strips must change dimensions in acircumferential direction. lf they are provided with electrodes on theirradial inner and outer surfaces, thereby presenting a comparatively lowelectrical impedance in the circuit in which they are connected, a lowelectro-mechanical coupling coefi'icient results. lf they are providedwith electrodes at their peripheral ends, so that they are polarizedcircumferentially, and hence in the same direction as their mechanicalexpansion and contraction, higher andrtherefore more desirableelectro-mechanical coupling coetiicients are Obtained, but theelectrical impedance is correspondingly increased, with a consequentloss in electrical effectiveness. The structure of the present inventionpermits the attainment of relatively high eiectro-mechanical couplingcoefficients, thus making for good transducing efiiciency, and at thesaine time, provides for relatively low electrical impedance, thusmaking for high overall efiiciency.

Structures of the type under discussion, particularly 3,142,035 PatentedJuly 2l., 1964 when designed for underwater operation, are adapted to becovered by a protective sheath of rubber or the like. If there are anygaps, even of the most minute nature, between this sheath and thetransducer ring itself, the mechanical transfer of vibratory energybetween the transducer ring and the medium in which it is placed willsuffer, thus reducing the overall efficiency of the devices. In anattempt to solve this problem, the prior art has often permanentlybonded the protective sheath to the ring. This, however, greatlyincreases the time and expense involved in maintenance and replacement,and is not always effective in eliminating gaps between sheath and ring.In accordance with the present invention, the transducer ring defined bythe strips of transducing material plus the other strips in the makeupof that ring form a structure the periphery of which is not trulycylindrical, but which may readily be covered by a thin layer of plasticmaterial which is bonded thereto. The outer surface of that layer may bemade truly cylindrical and exceptionally smooth. The protective rubbersheath may easily be slid over this outer surface, thus permitting readydisassembly of the transducer proper from the sheath, and because of theextreme smoothness of the outer surface of the thin plastic layer, thesheath and the ring will be in intimate physical, and thereforeacoustical, contact, thus insuring maximum transfer of energy.

In accordance with the above, the transducer ring is formed of aplurality of strips of appropriate transducing material, which may besubstantially rectangular in crosssection and hence easily and efcientlyformed. These transducing strips are provided at their sides facingcircumferentially along the ring with appropriate electrodes. interposedbetween selected pairs of these transducing strips are spacing stripspreferably formed of conductive material. The side surfaces of thesespacing strips facing circumferentially along the ring are so shaped andoriented as, when engaged by the electrode-covered side surfaces of theadjacent transducing strips, to cause the strips collectively to assumea substantially ring shape, and to cause the adjacent transducing stripsto be urged radially in a given direction relative to the ring when thering is compressed. The spacing strips and the adjacent transducingstrips are provided with cooperating parts which, when the ring iscompressed, prevent relative movement between those strips in theopposite radial direction. Consequently all of the strips will retaintheir proper radial and circumferential position.

In the form here specifically disclosed, the spacing strips have across-sectional shape comparable to that of a keystone, with ledgesformed thereon at the narrow end of the keystone. The inclination of thesides of the keystone prevent the transducing strips from movingradially outward and engagement between the transducing strips and theledges on the spacing strips prevent the transducing strips from movingradially inwardly. The relative positions of the strips are thereforefixed.

The combined cross-sectional areas of the spacing strips form anappreciable proportion of the total crosssectional area of the ring.Consequently, the physical characteristicsV of the material of which thespacing strips are formed will appreciably contribute to a determinationof the resonant frequency of the ring. Hence, that resonant frequencycan be varied within limits for a given size ring through judiciousselection of the material of which the spacing strips are formed, theuse of material of less stiffness giving rise to a lower resonantfrequency. The stiffness of spacing strips of a given material may alsobe lowered, thereby to lower the resonant frequency of the ring, byweakening the spacing strips as by providing passages therethrough.

The spacing strips, when conductive in nature, define electrical`terminals adapted to be electrically connected to an external source ofvoltage, and an electric circuit is defined from one conductive spacingstrip to the next conductive spacing strip in the ring via thetransducing strips located therebetween. Where minimization ofelectrical impedance is a factor, and whether the spacing strips areconductive or not, it is preferred to interpose a plurality ofindividual transducing strips between each pair of spacing strips, andto connect those transducing strips in parallel with one another. Thisis readily accomplished by interposing a thin conductive element such asa mesh sheet between each adjacent pair of transducing strips, thatelement being pressed into intimate physical and electrical connectionwith the electrodes on the sides of the transducing strips and extendingout radially beyond the ring, the radially extending portions of themesh sheets being electrically connected to electrical terminals ofappropriate polarity.

To the accomplishment of the above, and to such other objects as mayhereinafter appear, the present invention relates to the structure of anelectro-mechanical transducer, as dened in the appended claims and asdescribed in this specification, taken together with the accompanyingdrawings, in which:

FIGURE 1 is an elevational view of one embodiment of the presentinvention formed of a plurality of transducer rings disposed inlongitudinal coaxial array;

FIGURE 2 is a fragmentary cross-sectional view, on an enlarged scale,taken through one end of the device of FIGURE 1 as indicated by the line2 2 of FIGURE 3;

FIGURE 3 is a cross-sectional view taken along the line 3 3 of FIGURE 2,with certain parts omitted for purposes of clarity;

FIGURE 4 is a schematic view of a portion of the transducer ring ofFIGURE 3 illustrating the electrical connections;

FIGURE 5 is a schematic View similar to FIGURE 3, but showing analternate embodiment;

FIGURE 6 is a front elevational view of a conductive strip;

FIGURE 7 is an end elevational view thereof;

FIGURE 8 is a cross-sectional View, on an enlarged scale, taken alongthe line 8 8 of FIG. 3, semischematically indicating the manner in whichelectrical connection is made to the electrodes of adjacent transducingstrips;

FIGURE 9 is a front elevation view of a transducing strip; and

FIGURE 10 is a view as taken along the line 10 10 of FIGURE 8.

The transducer assembly illustrated in FIGURE 1 comprises a plurality ofcoaxially arranged individual transdusing rings, each generallydesignated by the reference numeral 2 (see FIG. 2). The assembly mayconsist of two sections designated 4 and 6, each connected at one end toan intermediate mounting bracket 8 and each having at its other end aunit 10 which seals off the end of the assembly and provides forelectrical connection to external circuitry. Each of the sections 4 and6 may consist of a plurality of individual transducer rings 2.

In the form specifically disclosed in FIGURES 3 and 4, the ring 2comprises a plurality of elongated transducing strips 12 and a pluralityof individual conductive spacing strips 14, all of equal length, therebeing three times as many transducing strips 12 as there are conductivestrips 14. The transducing strips 12 are shown as substantiallyrectangular in cross-section, and their side surfaces 16 aresubstantially parallel and are provided with conductive electrodes 18(see FIG. 8) over substantially their entire area. These transducingstrips 12 are formed of any appropriate transducing material, such asbarium titanate, and they are electrically polarized between theirelectrodes 18 as schematically indicated in FIGURES 3 and 4. As thepotential applied between these electrodes 18 variesin polarity, thewidth of the strips 12 (as measured between their electrode-covered sidesurfaces 16) will vary, or if the width of the strip is physicallyvaried, the potential across the electrodes 18 will vary.Electro-mechanical transducing therefore occurs.

The spacing strips 14 (see FIGS. 6 and 7) are formed of an appropriateconductive material, such as steel or brass. The conductive strips 14are provided with outer surfaces 20 from which side surfaces 22 extendin converging relation, the inner ends of those side surfaces 22terminating in outwardly disposed ledges 24 defined by protrusions 26.The inner surface of the conductive strips 14 may be grooved, as at 28,and a terminal lug 30, which may take the form of a brass tube, issecured to the strip 14 within the groove 28, as by being receivedwithin aperture 32, the lug 30 being located longitudinally olf-center,adjacent one end of the strip 14, and extending out beyond the groove 28formed in the inner surface thereof.

The shape of the conductive strips 14, and particularly the sidesurfaces 22andledges 24 thereon, is such as topermit one or more of thetransducing strips 12 to be interposed between a pair of conductivestrips 14 in such a manner as to insure that appropriate radial andcircumferential relationship between the strips will be maintained whenthe ring is formed. Thus, with reference specifically to FIGURE 3, thetransducing strip 12 immediately adjacent a given side of a conductivestrip 14 engages both the side surface 22 and ledge 24 of the latter,and in so doing is oriented so as to conform to the desired ring-shapeof the completed assembly of strips. Because of the inclination of theside surface 22 of the conductive strip 14, circumferential compressionof the ring will tend to cause the transducing strip 16 to move radiallyinwardly and will prevent radial outward movement of that strip 12.Radially inward movement of the strip 12 is positively prevented by theledge 24. Thus, the shape of the conductive strips 14 control, determineand reliably fix the circumferential and radial positions of all of thestrips 12 and 14. This is the case even when, as disclosed in FIGURE 5,only a single transducing strip 12 is interposed between each conductivestrip 14.

The conductive strips 14 function as electrical terminals with respectto the transducing strips positioned therebetween. To that end, eachalternate conductive strip 14 is electrically connected to have adierent polarity, as indicated in FIGURES 3, 4 and 5. To facilitate theattainment of this polarity, each alternate conductive strip 14 isarranged with its terminal lug 30 differently positioned, the terminallugs 30 on each set of conductive strips 14 of the same polarity beingat approximately the same level along the axis of the ring. Since theterminal lugs 30 are located nearer one end of the strips 14 than theother, this is readily accomplished by assembling the ring with onestrip 14 having its terminal lug 30 near the top of the ring, the nextstrip 14 having its terminal lug 30 near the bottom of the ring, and soon. Hence, one wire 32 may be connected between all of the terminal lugs30 of one set, and another wire 34 may be connected between all of theterminal lugs 30 of the other set, the wires 32 and 34 being connectedto external circuitry so as to have opposite polarity applied thereto atany given instant. (It will be understood, of course, that the signalsapplied to the wires 32 and 34 will usually be alternating in characterso that the polarity of those wires, and of the conductive strips 14 towhich they are connected, as indicated in FIGURES 3 and 4, represents aninstantaneous condition. The polarities of the transducing strips 12 asindicated in FIGS. 3 and 4 represent the permanent piezoelectricpolarization thereof.)

The basic mode of operation of the transducing ring 2 will in the mainbe apparent from the above description. The individual transducingstrips 12 are polarized in the direction of the circumference of thering 2, and as the polarity of the electrical potential applied to theelectrodes 18 is caused to vary, the corresponding dimension of thetransducing strips 12 will also vary, thus causing the ring to expandand contract. Since the dimensional change in the transducing strips 12is in the same direction as their electrical polarization, they operatein the 3-3 mode, and hence relatively high electro-mechanical couplingcoef'licients are obtained.

In the embodiment illustrated in FIGURE 5, the circumferential distancebetween adjacent conductive strips 14 is relatively small, and hence theeffective capacitance between those conductive strips 14 iscorrespondingly large, leading to relatively low impedance. In theembodiment of FIGURES 3 and 4, however, the circumferential spacingbetween adjacent conductive strips 14 is appreciably greater, and henceif a single transducing strip 12 were interposed therebetween, as in theembodiment of FIGURE 5, an excessively high electrical impedance betweenthe strips 14 might result. To avoid that undesirable eventuality, eachpair of conductive strips 14 has a plurality of transducing strips 12interposed therebetween, those transducing strips 12 being electricallyoppositely polarized as indicated. The strips 12 are adapted to beelectrically connected in parallel between the adjacent conductivestrips 14 in accordance with their respective electrical polarizations.With this mode of connection, each of the transducing strips 12 has acapacitance between its electrodes 18 which is approximately one-thirdof the value which would obtain if a single transducing strip wereemployed, and this reduction in capacitance, coupled with the parallelelectrical connection, results in an electrical impedance which is onlyapproximately one-ninth of that which would be obtained if a singletransducing strip 12 of comparable circumferential length were employed.Hence, optimum electro-mechanical efficiency and optimum electricalcharacteristics are achieved simultaneously.

To facilitate the parallel electrical connection of the plurality oftransducing strips 12 interposed between each pair of conductive strips14, a conductive sheet 36 formed of copper mesh is interposed betweeneach pair of adjacent transducing strips 12 in intimate physical andelectrical connection with the electrodes 18 over substantially thecomplete area of those electrodes, as may best be seen from FlGURE l0. Aportion 3S of this copper mesh sheet 36 extends radially inwardly beyondthe inner surfaces of the transducing strips 12. A buss wire 40 issoldered to the edge of the mesh portion 38 along substantially itsentire length, and a lead 42 is electrically connected to and extendsfrom the buss wire 46, the leads 42 extending to and being connected tothe terminal lugs Sti on the appropriate adjacent conductive strips 14.The function of the buss wire 4u is to ensure that substantially uniformelectrical polarity is applied over the entire area of the electrodes 1Sof the transducing strips 12.

Copper mesh sheets similar to the sheets 36 except that they do notextend radially beyond the ring 2 may be compressed between theconductive strips 14 and the transducing strips 12 adjacent thereto, inthe embodiments both of FIGURES 3 and 5, in order to facilitateelectrical connection between adjacent strips.

Assembling the rings 2 (see FIG. 2), the facing surfaces of the variousstrips 12 and 14 are cleaned and then coated with a suitable adhesive,usually of a heat-setting type. The strips 12 and 14 are laid out in agenerally circular pattern corresponding to that of the desired ring,and the mesh strips 36 are properly positioned between the electrodes 13of adjacent transducing strips 12. Clamps are then piaced around theoutside of the ring, preferably at spaced locations axially therealong,and tightened. This will cause all of the strips to be pressed intociose circumferential engagement with one another. The clamped ring isthen subjected to suitable heat treatment until the adhesive has set.

The inwardly projecting mesh portions 38 may be reinforced with plasticmaterial, such as epoxy resin, to rigidify them and prevent breakage.

If desired each set of three transducing strips 12 may be consolidatedinto subassemblies by bonding the strips to one another before suchsubassemblies are assembled to the spacing strips 14.

The outer surface of the thus-formed ring is not truly cylindrical, asmay be clearly seen from FIGURE 3. The ring 2 is therefore preferablypositioned Within a suitable mold having an extremely smooth andaccurately cylindrical inner surface, and the space between the ring 2and the mold is filled with a suitable coating material, such asbubble-free epoxy resin. This resin defines a coating 44 (see FIG. 2)which is bonded to the outside of the ring 2 and which has an outersurface which is substantially truly cylindrical and glassy-smooth.

The assembly of FIGURE l is formed by locating a ring 2 on insulatingbase plate 46 (see FIGS. 2 and 3) which is in turn mounted on end plate48, an insulating spacer 50 being positioned on top of the ring 2, thenext ring 2 being located on top of the spacer Sti, and so on to desiredaxial length. Sealing material (not shown) may be located between thering 2 and the elements 46 and 5t?. A steel cylinder 54 is also mountedon the end plate 4g, a space 56 being defined between it and the ring 2,within which space leads 58 and 60 are received which are connected toexternal circuitry in any appropriate manner, as by terminals 61, leads63, and glands 65. These leads 53 and 60 are in turn electricallyconnected to the wires 32 and 34 for each of the rings 2.

A rubber sheath or boot 62 is received over the periphery of the axiallyaligned rings 2. This sheath 62 engages the outer surface of the coating44 on the ring. Since that outer surface is smooth, the sheath 62 mayreadily be applied or removed, and when applied, it will engage thecoating 44 tightly and uniformly and without any cavities, pits or gapstherebetween. Hence, the sheath 62 will be an intimate and efficientacoustical contact with the ring 2, as is necessary if the device is tofunction in an eflicient manner.

The resonant frequency of each ring 2 will be determined by the physicalcharacteristics of the transducing strips 12 and the spacing strips 14.Since the transducing strips 12 must be made of materials havingappropriate electro-mechanical characteristics, and since there are onlya limited number of such materials available, there is not much that canbe done to control the resonant frequency insofar as the transducingstrips 12 are concerned except by making the ring 2 of appropriatediameter and thickness. However, the presence of the spacing strips 14,the total cross sectional area of which constitutes an appreciableproportion (which may range between 5% and 40%, and is preferablybetween 10% and 25%) of the total cross sectional area of the completering 2, permits control of the resonant frequency of the ring 2 withoutchanging its dimensions, but rather by changing the overall stiffness ofthe spacing strips 14. This variation may be accomplished in severalways. Different materials may be used for the spacing strips 14.v Feweror more spacing strips 12, or spacing strips of greater or lesser crosssection, may be used. The use of brass instead of steel will reduce theresonant frequency. The use of a lead alloy will still further reducethe resonant frequency, because of its low stiffness and high density.The stiffness of the spacing strips 14 can be modified by formingpassages therethrough, such as the axially extending apertures 64 shownin FIGURE 5, the presence of the passages 64 causing a further reductionin the resonant frequency of the ring.

The electrical conductivity of the lead alloy is satisfactory, but ifdesired for any reason, as if strips 14 were not satisfactorilyconductive, means other than the strips 14 alone may be used to makeelectrical connection with the transducing strip electrodes 13 adjacentthe strips 14. Hence, although the strips 14 have often here been termedH conductive strips, since they usually have that characteristic, it isnot essential that they be conductive. They can be considered moregenerically as spacing strips interposed between predetermined numbersof transducing strips.

By way of example, a typical one foot diameter ring with a one inch wallthickness employing twelve 3-bar ceramic (barium titanate) strips and 12steel conductive strips 14, as in FIGURE 3, would have a resonantfrequency of about 5 kc. By changing the steel conductive strips 14 tobrass strips, the resonant frequency would be reduced to approximately4.5 kc. By forming the apertures 64 such as shown in FIGURE 5, theresonant frequency would be reduced still further to approximately 4 kc.This reduction in resonant frequency is accomplished Without change inthe overall dimensions of the unit and without adversely changing theacoustic behavior of the device.

From the above it will be apparent that the cooperation between thespacing strips 14 and the transducing strips 12 greatly facilitatesassembly of the ring 2. Once the strips have been initially assembled ina roughly ring Shape, the engaging side surfaces of the strips act in acam-like manner to force the several strips into proper position as theloosely assembled ring is compressed into iinal shape. The greater thecompressive force exerted on the ring, the greater is the force urgingthe strips into their proper relative positions. The fact that this willoccur even when transducing strips 12 of substantially rectangularcross-section are employed is noteworthy. The spacing strips 14 whichthus facilitate the assembly of the ring serve other importantfunctions. They contribute appreciably to a determination of theresonant frequency of the ring 2, thus permitting the attainment, withinlimits, of different resonant frequencies for rings of the same size.The spacing strips 14 may be made of conductive material, in which casethey can serve as terminals by means of which electrical connection ismade to the transducing strips 12. By placing a plurality 0f transducingstrips 12 between each adjacent pair of spacing strips 14, and byconnecting those transducing strips 12 in parallel, the strips 12 haveappropriate electrical polarization, optimum electrical andelectro-mechanical eiciency is obtained. By covering the outer surfaceof the ring formed by the strips with a thin layer of plastic materialbonded to the strips, the thus-formed ring can be given a cylindrical,glassy-smooth outer surface which facilitates assembly and disassemblywith the covering sheath 62 and ensures that the sheath 62 will be inclose acoustical engagement therewith.

While but a limited number of embodiments of the instant invention havebeen here specifically disclosed, it will be apparent that manyvariations may be made therein, all within the scope of the invention asdefined in the following claims.

I claim:

1. A transducer comprising a plurality of strips of transducing materialand a plurality of spacing strips interposed between selectedtransducing strips, said strips collectively deiining a substantiallyring-shaped structure, said spacing strips having non-parallel sidesurfaces terminating at one end in substantially laterally extendingledges, said transducing strips being in operative engagement with saidside surfaces and being retained in position by said ledges.

2. The transducer of claim 1, in which said spacing strips are providedwith passages, thereby to modify the resonant frequency of saidtransducer.

3. The transducer of claim 2, in which the collective cross-sectionalarea of said spacing strips denes a substantial proportion of the totalcross-sectional area of said ring, whereby the physical characteristicsof said spacing strips contribute appreciably to the determination ofthe resonant frequency of said transducer.

4. The transducer of claim l, in which the collective cross-sectionalarea of said spacing strips defines a substantial proportion of thetotal cross-sectional area of said ring, whereby the physicalcharacteristics of said spacing strips contribute appreciably to thedetermination of the resonant frequency of said transducer.

5. The transducer of claim l, in which a plurality of said transducingstrips are interposed between each pair of spacing strips and areelectrically connected in parallel.

6. The transducer of claim 5, in which a thin conductive element isinterposed between each pair of adjacent transducing strips, saidelement being in electrical connection With said transducing strips andextending radially beyond said transducing strips, said electricalconnections to said transducing strips comprising said elements.

7. A transducer comprising a plurality of strips of transducing materialand a plurality of spacing strips interposed between selectedtransducing strips, said strips collectively defining a substantiallyring-shaped structure, said spacing strips being essentially ofkeystone-shape in cross-section and having laterally extending ledges atthe narrow end of said keystone shape, said transducing strips being inoperative engagement with the side surfaces of said spacing strips andbeing retained in position by said ledges.

8- The transducer of claim 7, in which spacing strips are provided withpassages, thereby to modify the resonant frequency of said transducer.

9. The transducer of claim 8, in which the collective cross-sectionalarea of said spacing strips defines a substantial proportion of thetotal cross-sectional area of said ring, whereby the physicalcharacteristics of said spacing strips contribute appreciably to thedetermination of the resonant frequency of said transducer.

10. The transducer of claim 7, in which the collective cross-sectionalarea of said spacing strips denes a substantial proportion of the totalcross-sectional area of said ring, whereby the physical characteristicsof said spacing strips contribute appreciably to the determination ofthe resonant frequency of said transducer.

ll. The transducer of claim 7, in which a plurality of said transducingstrips are interposed between each pair of spacing strips and areelectrically connected in parallel.

l2. The transducer of claim 11, in which a thin conductive element isinterposed between each pair of adjacent transducing strips, saidelement being in electrical connection with said transducing strips andextending radially beyond said transducing strips, said electricalconnections to said transducing strips comprising said elements.

13. A transducer comprising a plurality of strips of transducingmaterial and a plurality of spacing strips of conductive material, saidstrips collectively defining a substantially ring-shaped structure, aplurality of said transducing strips being arranged circumferentiallybetween each pair of spacing strips and electrically connected inparallel between said pairs of spacing strips.

14. A transducer comprising a plurality of strips of transducingmaterial having essentially parallel side surfaces, and a plurality ofspacing strips interposed between selected transducing strips, saidstrips collectively defining a substantially ring-shaped structure7 saidside surfaces of said selected transducing strips being in operativeengagement with the side surfaces of said spacing strips, said sidesurfaces of said spacing strips being inclined to prevent movement ofsaid transducing strips radially of said ring in one direction, andcooperating parts on said spacing strips and said selected transducingstrips for preventing movement of said transducing strips radially ofsaid ring in the other direction.

(Other references on following page) 9 UNITED STATES PATENTS HarrisonFeb. 25, Benioi Apr. 22, Lanphier July 11, Massa Sept. 4, Ely July 31,Harris Jan. 21,

Cil

OTHER REFERENCES Rand et al.: Proceedings of the National ElectronicsConference, 1958, vol. 14, pages 180481.

13. A TRANSDUCER COMPRISING A PLURALITY OF STRIPS OF TRANSDUCING MATERIAL AND A PLURALITY OF SPACING STRIPS OF CONDUCTIVE MATERIAL, SAID STRIPS COLLECTIVELY DEFINING A SUBSTANTIALLY RING-SHAPED STRUCTURE, A PLURALITY OF SAID TRANSDUCING STRIPS BEING ARRANGED CIRCUMFERENTIALLY BETWEEN EACH PAIR OF SPACING STRIPS AND ELECTRICALLY CONNECTED IN PARALLEL BETWEEN SAID PAIR OF SPACING STRIPS. 